1. Field of the Invention
The present invention relates to a switching apparatus for switching real-time packets in real time and a packet switching method.
2. Description of the Related Art
In best effort networks adopting a carrier sense multiple access with collision detection (CSMA/CD) method or a full duplex method, demand for transmission of real-time data streams, such as sounds or videos, has been increased.
However, due to the characteristics of the best effort networks, it is difficult to reliably transmit a predetermined number of real-time streams (information) including videos or sounds within a predetermined time. This difficulty is a problem of assuring the quality of service (QoS) for real-time applications. This assurance is broadly divided into four aspects: that is, delay assurance, delay distribution assurance, bandwidth assurance, and packet loss assurance. In order to realize these aspects of the assurance, the following four technical elements (a) to (d) are provided.
(a) Classifier
Classifier is a method of grouping the traffic of received packets based on the source, destination, transmission control protocol/user datagram protocol (TCP/UDP) port number, and Type of Service (ToS) field in a router or a switch.
(b) Admission Control
Admission control is a method of controlling the reservation of resources for every session. Before a session is started, a resource on a path is reserved by a resource reservation setup protocol. When the reservation fails, the session is not started.
(c) Packet Scheduler
Packet scheduler is a method of adjusting the schedule of transmission of packets divided into groups. The packet scheduler is realized by various methods, such as a queuing method and a buffer control method.
(d) Traffic Shaper
Traffic shaper is a technique of smoothing input burst traffic in a constant rate.
Models for realizing these technical elements include integrated services (Int-serv), a resource reservation protocol (RSVP), and differentiated services (Diff-serv).
A network terminal that intends to process real-time stream data including sounds or videos makes reservation of a resource in a network or a network management entity according to procedures defined in the above models. The network that accepts the reservation performs the classifier, the admission control, and the packet scheduler, which are the technical elements described above, in a router or a switch in the network to try to ensure the QoS.
The network terminal must perform traffic shaping within the range of the reserved resource.
In order to ensure the delay distribution from the source to the destination of a real-time data packet in a switch in the network, that is, in order to limit the delay variation within a certain range, the technical elements including the classifier, the admission control, and the packet scheduler are necessary. The packet scheduler is, for example, a strict priority scheduler, a weighted fair queuing (WFQ) scheduler, or a deficit round robin (DRR) scheduler.
When the switch strictly and absolutely gives priority to the real-time stream data, the strict priority scheduler is used. In the strict priority scheduler, the switch must know the generation cycle and generation time of the real-time data packets by using some kind of means in order to reserve resources for the real-time data packets, which are periodically generated.
To this end, the generation cycle and generation time of the real-time data packets are set in advance in a normal switch, the switch acquires the information concerning the generation cycle and generation time of the packets in the switched real-time channels from the centralized management entity managing the real-time channels, or the switch acquires the information concerning the generation cycle and generation time of the real-time data packets from the terminal that generates the real-time stream at the start of the stream.
However, there is a problem in that a procedure in which the management entity manages the information concerning the entire network or each network switch and sets the information in the corresponding switch before or after the real-time stream is generated is very complicated, regardless of the size of the network. The information concerning the entire network includes the number of the real-time channels in the network and the path of the real-time channels. The information concerning each network switch includes the generation cycle and generation time of the real-time data packets.